Maximum stresses in mooring lines during parametric excitation

The ferry links crossing the fjords along the west coast of Norway are going to be replaced by fixed links. Among the proposed solutions is the construction of Submerged Floating Tunnels (SFT). A mooring system should be used to restrain the movements of these floating structures. Long period waves, such as swell waves, parametrically excite the system and might result in excessive vibrations in the cable. Relevant literature have extensively analyzed the lateral motions during parametric resonance. However, it is unclear how parametric excitation affects the stresses along the mooring line. The existing studies investigating the actual stresses developed during such violent situations are limited. Additional studies are deemed necessary for the safe design of this crucial element in SFT. Maximum tension and bending moments might vary in magnitude and location during parametric resonance. Thus, this paper investigates the maximum total stresses along the tether due to the combination of both spatial- and time-varying forces. The aim of this paper is to assess the necessity of using the stability charts for the design of mooring lines with respect to safe levels of cable stresses. This is achieved through the numerical analysis of a submerged cable model using Abaqus. Cable vibrations, forces and stresses are analyzed and compared for a range of amplitudes and frequencies of the support motions.